Reactions where a first reactant, dissolved in a liquid, reacts with a second reactant contained in a gas under increased surface area conditions are known to the art. Such reactions are carried out in devices as scrubbers, burners, reaction vessels, and the like, for example.
Atomization of liquids into a gaseous atmosphere is one of the above mentioned techniques described in the art. The atomization techniques for conducting reactions, disclosed in the art so far, are rather crude and lack innovative features for controlling such reactions with respect to: desired reaction product if the reaction product is an intermediate, yield in reaction product, conversion and conversion rate, temperature profiles in the reaction zone, average droplet size or diameter, evaporation rates, and the like. Actually in most, if not all, cases, the reaction product is substantially the final product expected under the crude overall conditions of the reaction. For example, in the case of a burner, where a fuel is atomized into an atmosphere of an oxygen-containing gas (such as air for example), the final product of reaction is carbon dioxide, with desired minimization of carbon monoxide and nitrogen oxides as much as possible. In another example, a scrubber for removing acidic compounds from a gas may use an atomized liquid containing alkali or alkaline earth compounds which react with the acidic compounds in the gas to form the corresponding salts. In still another example, ammonia and phosphoric acid react under atomization conditions to form ammonium orthophosphate, which is a final reaction product.
On the other hand, reactions which are geared to produce intermediate products, especially in the case of oxidations, are not run under atomization conditions, since atomization promotes complete reactions to a final product. For example, oxidation of cyclohexane to adipic acid, or oxidation of p-xylene to terephthalic acid, have not been reported to be conducted under atomization conditions, and there is no incentive in the art to do so, since burning of cyclohexane to carbon dioxide has been expected to take place under such conditions. However, the inventors have discovered that in the presence of unexpected intricate critical controls and requirements of the instant invention, intermediate reaction or oxidation products, such as adipic acid, phthalic acid, isophthalic acid and terephthalic acid, for example, may be advantageously obtained under atomization conditions.
The following references, among others, describe processes conducted in intermixing liquid with gaseous materials, mostly under increased surface area conditions.
U.S. Pat. No. 5,399,750 (Brunet al.) discloses methods for preparing maleamic acid (aminomaleic acid) by reacting gaseous ammonia with molten maleic anhydride under reactant contact conditions of high surface area, for example reacting said gaseous NH.sub.3 with a thin film of said molten maleic anhydride or with said molten maleic anhydride in a state of vigorous agitation.
U.S. Pat. No. 5,396,850 (Conochie et al.) discloses a method of destroying organic waste in a bath of molten metal and slag contained in a vessel. The method comprises injecting organic waste into the bath to form a primary reaction zone in which the organic waste is thermally cracked and the products of the thermal cracking which are not absorbed into the bath are released into the space above the surface of the bath. The method further comprises injecting an oxygen-containing gas toward the surface of the bath to form a secondary reaction zone in the space above the surface of the bath in which the oxidizable materials in the products from the primary reaction zone are completely oxidized and the heat released by such oxidation is transferred to the bath. In order to facilitate efficient heat transfer from the second reaction zone to the bath, the method further comprises injecting an inert or other suitable gas into the bath to cause molten metal and slag to be ejected upwardly from the bath into the secondary reaction zone.
U.S. Pat. No. 5,312,567 (Kozma et al.) discloses a complex mixing system with stages consisting of propeller mixers of high diameter ratio, where the blades are provided with flow modifying elements, whereby the energy proportions spent on dispersion of the amount of gas injected into the reactor, homogenization of the multi-phase mixtures, suspension of solid particles, etc. and the properties corresponding to the rheological properties of the gas-liquid mixtures and to the special requirements of the processes can be ensured even in extreme cases. Open channels opposite to the direction of rotation are on the blades of the dispersing stage of the propeller mixers fixed to a common shaft, where the channels are interconnected with gas inlet. The angle of incidence of a certain part of the blades of mixing stages used for homogenization and suspension is of opposite direction and the length is shorter and/or the angle of incidence is smaller than those of the other blades. Baffle bars are on the trailing end of the blades on a certain part of the propeller mixers used similarly for homogenization and suspension, and/or auxiliary blades at an angle of max. 20.degree. to the blade wings are arranged above or below the trailing end of the blades.
U.S. Pat. No. 5,244,603 (Davis) discloses a gas-liquid mixing system which employs an impeller/draft tube assembly submerged in liquid. Hollow eductor tubes affixed to the impeller drive shaft are used to flow gas from an overhead gas space to the liquid in the vicinity of the assembly. The positioning and size of the eductor tubes are such as to maximize the desired gas-liquid mixing and reaction rate.
U.S. Pat. No. 5,270,019 (Melton et al.) discloses an elongated, generally vertically extending concurrent reactor vessel for the production of hypochlorous acid by the mixing and reaction of a liquid alkali metal hydroxide and a gaseous halogen, wherein an atomizer is mounted near the top of the reactor vessel to atomize the liquid alkali metal hydroxide into droplets in the vessel. The vessel has a spraying and reaction zone immediately beneath the atomizer and a drying zone beneath the spraying and reaction zone to produce a gaseous hypochlorous acid and a substantially dry solid salt by-product.
U.S. Pat. No. 5,170,727 (Nielsen) discloses a processes and apparatus in which supercritical fluids are used as viscosity reduction diluents for liquid fuels or waste materials which are then spray atomized into a combustion chamber. The addition of supercritical fluid to the liquid fuel and/or waste material allows viscous petroleum fractions and other liquids such as viscous waste materials that are too viscous to be atomized (or to be atomized well) to now be atomized by this invention by achieving viscosity reduction and allowing the fuel to produce a combustible spray and improved combustion efficiency. Moreover, the present invention also allows liquid fuels that have suitable viscosities to be better utilized as a fuel by achieving further viscosity reduction that improves atomization still further by reducing droplet size which enhances evaporation of the fuel from the droplets.
U.S. Pat. No. 5,123,936 (Stone et al.) discloses a process and apparatus for removing fine particulate matter and vapors from a process exhaust air stream, and particularly those emitted during post-production curing or post-treatment of foamed plastics, such as polyurethane foam, in which the exhaust air stream is passed through a transfer duct into which is introduced a water spray in the form of a mist of fine droplets in an amount which exceeds the saturation point; thereafter the exhaust air stream is introduced into a filter chamber having a cross-sectional area that is substantially greater than that of the transfer duct, and the exhaust air stream passes through at least one, and preferably a plurality of high surface area filters, whereby a portion of the water is removed from the exhaust air stream and collected in the filter chamber prior to the discharge of the exhaust air stream into the environment.
U.S. Pat. No. 5,061,453 (Krippl et al.) discloses an apparatus for continuously charging a liquid reactant with a gas. The gas is dispersed in the reactant through a hollow stirrer in a gassing tank. The quantity of gas introduced per unit time is kept constant.
U.S. Pat. No. 4,423,018 (Lester, Jr. et al.) discloses a process according to which a by-product stream from the production of adipic acid from cyclohexane, containing glutaric acid, succinic acid and adipic acid, is employed as a buffer in lime or limestone flue gas scrubbing for the removal of sulfur dioxide from combustion gases.
U.S. Pat. No. 4,370,304 (Hendriks et al.) discloses methods by which ammonium orthophosphate products are prepared by reacting ammonia and phosphoric acid together at high speed under vigorous mixing conditions by spraying the reactants through a two-phase, dual coaxial mixer/sprayer and separately controlling the supply and axial outflow rate of the phosphoric acid at 1 to 10 m/sec. and the outflow rate of ammonia at 200 to 1000 m/sec. (N.T.P.). Thorough mixing and a homogenous product is obtained by directing the outflow spray into a coaxial cylindrical reaction chamber of a specified size with respect to the diameter of the outermost duct of the sprayer/mixer. The product may be granulated on a moving bed of granules and adjusted in respect of the NH.sub.3 to H.sub.3 PO.sub.4 content by changing the concentration of the phosphoric acid and/or supplying additional ammonia to the granulation bed.
U.S. Pat. No. 4,361,965 (Goumondy et al.) discloses a device for atomizing a reaction mixture, said device enabling the reaction mixture to be atomized in a reactor with the aid of at least a first gas and an atomizing nozzle. This device further comprises a supply of a second hot gas at the top of the atomizing device, serving to dry the atomized mixture, a supply of a third gas and means for distributing this third gas comprising an annular space of adjustable width and adapted to distribute in the reactor said third gas in the form of a ring along the inner wall of the reactor, so as to avoid any contact between the reaction mixture and said wall. The invention is applicable to the atomization of a reaction mixture.
U.S. Pat. No. 4,308,037 (Meissner et al.) discloses methods according to which high temperature thermal exchange between molten liquid and a gas stream is effected by generating in a confined flow passageway a plurality of droplets of molten liquid and by passing a stream through the passageway in heat exchange relationship with the droplets. The droplets are recovered and adjusted to a predetermined temperature by means of thermal exchange with an external source for recycle. The process provides for removal of undesired solid, liquid or gaseous components.
U.S. Pat. No. 4,065,527 (Graber) discloses an apparatus and a method for handling a gas and a liquid in a manner to cause a specific interaction between them. The gas is placed into circulation to cause it to make a liquid circulate in a vortex fashion to present a liquid curtain. The gas is then passed through the liquid curtain by angled vanes to cause the interaction between the two fluids, such as the heating of the liquid, scrubbing of the gas, adding a chemical to the liquid and the like. The vanes are spaced apart and project inwardly from the inner periphery of an annular support so that the circulating liquid readily moves into the spaces between the vanes to create the liquid curtain. A number of embodiments of the invention are disclosed.
U.S. Pat. No. 4,039,304 (Bechthold et al.) discloses methods according to which waste gas is contacted with a solution of a salt from a pollutant of the gas. This solution is obtained from another stage of the process used for cleaning or purifying the gas. The resulting mixture of gas and solution is subjected to vaporization so as to obtain a dry gaseous substance constituted by the waste gas and the evaporated solvent for the salt. The gaseous substance thus formed contains crystals of the salt as well as the pollutant present in the original waste gas. The salt crystals and other solid particles are removed from the gaseous substance in the form of a dry solids mixture. The gaseous substance is subsequently mixed with an absorption fluid such as an ammonia solution in order to wash out and redissolve any salt crystals which may remain in the gaseous substance and in order to remove the pollutant present in the original waste gas from the gaseous substance. The pollutant and the redissolved salt crystals form a salt solution together with the absorption fluid and it is this salt solution which is brought into contact with the waste gas. The gaseous substance is exhausted to the atmosphere after being mixed with the absorption fluid.
U.S. Pat. No. 3,928,005 (Laslo) discloses a method and apparatus for treating gaseous pollutants such as sulfur dioxide in a gas stream which includes a wet scrubber wherein a compressed gas is used to atomize the scrubbing liquid and a nozzle and the compressed gas direct the atomized liquid countercurrent to the flow of gas to be cleaned. The method and apparatus includes pneumatically conveying to the nozzle a material such as a solid particulate material which reacts with or modifies the pollutant to be removed or altered. The gas used for atomizing the scrubbing liquid is also used as a transport vehicle for the solid particulate material. In the case of sulfur oxides, the material may be pulverized limestone.
U.S. Pat. No. 3,677,696 (Helsinki et al) discloses a method according to which, the concentration of circulating sulfuric acid is adjusted to 80-98% by weight and used to wash hot gases containing mercury. The temperature of the acid is maintained between 70.degree.-250.degree. C., and the solid material separating from the circulating wash solution is recovered.
U.S. Pat. No. 3,613,333 (Gardenier) discloses a process and apparatus for removing contaminants from and pumping a gas stream comprising indirectly heat exchanging the gas and a liquid, introducing the liquid under conditions of elevated temperature and pressure in vaporized and atomized form into the gas, mixing same thereby entrapping the contaminants, and separating clean gas from the atomized liquid containing the contaminants.
U.S. Pat. No. 2,980,523 (Dille et al.) discloses a process for the production of carbon monoxide and hydrogen from carbonaceous fuels by reaction with oxygen. In one of its more specific aspects it is directed to a method of separating carbonaceous solid entrained in the gaseous products of reaction of carbonaceous fuels and oxygen wherein said products are contacted with a limited amount of liquid hydrocarbon and thereafter scrubbed with water, and said carbonaceous solid is decanted from said clarified water.
U.S. Pat. No. 2,301,240 (Leuna et al.) discloses an improved process for removing impurities from acetylene gas which has been prepared by thermal or electrical methods by washing with organic liquids, as for example oils or tars.
U.S. Pat. No. 2,014,044 (Haswell) discloses an improved method for treating gas and aims to provide for the conservation of the sensible heat of such gas.
U.S. Pat. No. 1,121,532 (Newberry) discloses a processes of recovering alkalis from flue-gases.
Currently, oxidation reactions for the production of organic acids, including but not limited to adipic acid, are conducted in a liquid phase reactor with reactant gas sparging. The reactant gas in these cases is typically air, but may also be oxygen. Sufficient reactant gas, with or without non-reactive diluents (e.g., nitrogen), is sparged--at relatively high rate--so that the liquid reaction medium is aerated to maximum capacity (typically 15-25% aeration). The relatively high sparging rates of reactant containing gas feed (hereinafter referred to as "reactant gas"), associated with this conventional approach, have several drawbacks:
Costly reactant gas feed compressors are required to compress makeup reactant gas for sparging. These are expensive to install and operate (high electric or steam consumption), and have many utility problems resulting in excessive plant downtime. PA1 The required high gas rate makes it extremely difficult to control oxygen content in the reactor at low concentrations (due to the high reactor gas turnover rate). PA1 The required high gas rate makes it extremely difficult to control reaction temperature at low production rates (i.e., high turndown rate) for a given sized reactor system. This occurs because the gas used for sparging removes energy from the reaction system by volatilizing reaction liquid and liquid solvent--this volatilization effect is quite significant at the relatively high temperatures commonly associated with and required for oxidation reactions. Unless carefully balanced by an exothermic heat of reaction, this volatilization will act to substantially lower the temperature of the liquid content of the reactor. Thus, a properly sparged system can be designed for good temperature control at medium to high production rates, but will suffer temperature loss and loss of temperature control at significant turndown rate. PA1 High reactant gas feed rate results in relatively high reactor non-condensible off-gas rate. Non-condensible off-gases must either be totally purged to atmosphere, or--if oxygen content is high--partially purged and partially recycled to the reactor. The use of air as a reactant gas feed has drawbacks because it results in high rate of purge to the atmosphere--this is undesirable because this purge must first be cleaned in very expensive off-gas cleanup facilities in order to meet ever more stringent environmental requirements. The use of oxygen-only gas feed to the reactor may be undesirable because high sparging requirements result in low oxygen conversion in the reactor; low conversion results in high oxygen concentration within the reactor; and high oxygen concentration within the reactor may result in excessive over-oxidation of liquid reactants and liquid solvents with attendant high chemical yield loss (i.e., burning these to carbon monoxide and carbon dioxide). If the oxygen in the reactor is diluted with recycle nitrogen or gaseous-recycle inerts, then both high recompression investment and costs, and recompression utility problems are introduced. PA1 to increase reaction rate by increasing the mass transfer rate of gaseous reactants (oxygen) to liquid reaction sites; and PA1 so as to enable economic operation at relatively low oxygen concentration in the gas phase. PA1 (1) reacting, at a cycloaliphatic hydrocarbon conversion level of between about 7% and about 30%, PA1 (2) isolating the C.sub.5 -C.sub.8 aliphatic dibasic acid. PA1 atomizing the first liquid to form a plurality of droplets in the gas at an atomization temperature and at an atomization distance from a mass of a second liquid; PA1 causing a substantially non-destructive oxidation at an oxidation pressure between the first reactant and the oxidant to form the intermediate oxidation product; PA1 coalescing the droplets into the mass of the second liquid; PA1 controlling transient conversion of the first reactant and the oxidant to intermediate oxidation product in the droplets to be within a predetermined pre-coalescing transient conversion range, before said droplets coalesce into the second liquid; and PA1 separating the intermediate oxidation product from the second liquid. PA1 changing the atomization temperature, PA1 changing the reaction pressure, PA1 changing the atomization distance, PA1 changing the average droplet diameter, PA1 changing the first flow rate, PA1 changing the second flow rate, PA1 changing the volatilization rate, PA1 changing the first content, PA1 changing the second content, and PA1 a combination thereof. PA1 the first reactant comprises a compound selected from a group consisting of cyclohexane, cyclohexanone, cyclohexylhydroxyperoxide, cyclohexanol, o-xylene, m-xylene, p-xylene, a mixture of at least two of cyclohexane, cyclohexanone, cyclohexanol, and cyclohexylhydroxyperoxide, and a mixture of at least two of o-xylene, p-xylene, and m-xylene. PA1 the oxidant comprises oxygen; and PA1 a major portion of the reaction product comprises a compound selected from a group consisting of adipic acid, cyclohexanol, cyclohexanone, cyclohexylhydroperoxide, phthalic acid, isophthalic acid, terephthalic, a mixture of at least two of adipic acid, cyclohexanone, cyclohexanol, and cyclohexylhydroxyperoxide, and a mixture of at least two of phthalic acid, isophthalic acid, and terephthalic acid. PA1 atomizing a solution comprising metal ions of the lower valance state to form a plurality of droplets in a gas containing an oxidant; PA1 causing at least partial oxidation of the lower valance state ions to ions of higher valance state in the solution.
The current technology also suffers from a relatively low ratio of gas-liquid surface area to liquid reaction mass. The presently available art does not maximize this ratio. In contrast, the present invention maximizes said ratio in order:
Operating at lower oxygen concentration with acceptable conversion rates in the reactor improves yield by reducing over-oxidations, and eliminates safety (explosion) problems associated with operation in the explosive oxygen/fuel envelope. In the current technology, reducing oxygen content below traditional levels would result in a non-economic reduction in reaction rate. However, a significant increase in the aforementioned ratio--relative to current levels--would offset this rate reduction thereby enabling economic operation at reduced oxygen concentration in the reactor.
Another problem with the current technology is the sometimes formation of large agglomerations of insoluble oxidation products in the reactor. These can build up on reactor walls resulting in decreased available reaction volume, and in unwanted by-product formation due to over-exposure of said accretions to reaction conditions (e.g., high temperature) in oxygen-starved micro-reactor environments. These can also form large diameter, heavy solids in the reactor which can result in damage to expensive reactor agitator shafts and agitator seals resulting in costly repairs and high utility wear-problems. Finally, the current technology often requires expensive agitation shafts and seals capable of withstanding corrosive chemical attack and containing high system pressures.
Substituting gas-phase reaction systems for liquid-phase reactors introduces new problems, chief among which is the difficulty of identifying a cost-effective, efficient, non-plugging, long-lived catalyst system. Liquid-phase catalyst systems are well-developed and well-understood. Unfortunately, these are non-volatile. Using a non-volatile catalyst in a gas-phase reaction system must necessarily often be subject to severe plugging problems as most organic acids resulting from oxidation reactions are non-volatile solids--unless dissolved in a liquid reaction medium.
There is a plethora of references dealing with oxidation of organic compounds to produce acids, such as, for example, adipic acid.
The following references, among the plethora of others, may be considered as representative of oxidation processes relative to the preparation of diacids.
U.S. Pat. No. 5,321,157 (Kollar) discloses a process for the preparation of C.sub.5 -C.sub.8 aliphatic dibasic acids through oxidation of corresponding saturated cycloaliphatic hydrocarbons by
(a) at least one saturated cycloaliphatic hydrocarbon having from 5 to 8 ring carbon atoms in the liquid phase and PA2 (b) an excess of oxygen gas or an oxygen containing gas mixture in the presence of PA2 (c) less than 1.5% moles of a solvent per mole of cycloaliphatic hydrocarbon (a), wherein said solvent comprises an organic acid containing only primary and/or secondary hydrogen atoms and PA2 (d) at least about 0.002 mole per 1000 grams of reaction mixture of a poly valent heavy metal catalyst; and
U.S. Pat. No. 5,221,800 (Park et al.) discloses a process for the manufacture of adipic acid, according to which cyclohexane is oxidized in an aliphatic monobasic acid solvent in the presence of a soluble cobalt salt wherein water is continuously or intermittently added to the reaction system after the initiation of oxidation of cyclohexane as indicated by a suitable means of detection, and wherein the reaction is conducted at a temperature of about 50.degree. C. to 150.degree. C., at an oxygen partial pressure of about 50 to about 420 pounds per square inch absolute.
The following references, among others, describe oxidation processes conducted in multi-stage and multi-plate systems.
U.S. Pat. No. 3,987,100 (Barnette et al.) describes a process of oxidizing cyclohexane to produce cyclohexanone and cyclohexanol, said process comprising contacting a stream of liquid cyclohexane with oxygen in each of at least three successive oxidation stages by introducing into each stage a mixture of gases comprising molecular oxygen and an inert gas.
U.S. Pat. No. 3,957,876 (Rapoport et al.) describes a process for the preparation cyclohexyl hydroperoxide substantially free of other peroxides by oxidation of cyclohexane containing a cyclohexane soluble cobalt salt in a zoned oxidation process in which an oxygen containing gas is fed to each zone in the oxidation section in an amount in excess of that which will react under the conditions of that zone.
U.S. Pat. No. 3,530,185 (Pugi) describes a process for manufacturing precursors of adipic acid by oxidation of an oxygen containing inert gas which process is conducted in at least three successive oxidation stages by passing a stream of liquid cyclohexane maintained at a temperature in the range of 140.degree. to 200.degree. C., and a pressure in the range of 50-350 psig through each successive oxidation stage in an amount such that substantially all the oxygen introduced into each stage is consumed in that stage thereafter causing the residual inert gases to pass countercurrent into the stream of liquid during the passage of the stream through said stages.
None of the above references, or any other references known to the inventors disclose, suggest or imply, singly or in combination, oxidation reactions to intermediate oxidation products under atomization conditions subject to the intricate and critical controls and requirements of the instant invention as described and claimed.